Transducers for measuring ultra-high pressures, in the order of several hundred to several thousand atmospheres or more, are known, but they tend to be relatively massive and expensive.
For measuring lower pressures, in the order of 1,000 psi or less, reference is made to the capacitive pressure transducer assemblies and circuitry shown in U.S. Pat. No. 4,388,668 granted Jun. 14, 1983, U.S. Pat. No. 4,398,426, granted Aug. 16, 1983 and U.S. Pat. No. 4,227,419, granted Oct. 14, 1980, all of which are assigned to the assignee of the present invention. In the transducers shown in these patents, a thin diaphragm of low hysteresis insulating material, such as glass, or a ceramic such as alumina, is employed; and when pressure is applied to the diaphragm it flexes toward an adjacent base member, normally of the same material, and conductive layers forming electrodes on the facing surfaces change their spacing, thereby varying the capacitance between the two conductive-layer electrodes. Circuitry included in the transducer converts the capacitance changes to an electrical signal varying linearly with the pressure changes. These pressure transducers are relatively inexpensive and have been widely used in automotive control and other applications.
Transducers for pressure ranges up to about 1000 psi have been made using substantially the arrangements shown in the above cited patents. However, at pressures substantially above 1,000 psi, corresponding to more than 60 or 70 atmospheres or bars, standard low pressure transducer configurations are not entirely practical, as the pressure seals and other components cannot handle the very high pressures.
An effective high pressure transducer, also assigned to the assignee of the present invention, and operable up to about 10,000 psi is disclosed in U.S. Pat. No. 4,617,607, granted Oct. 14, 1986. In that transducer the pressure is primarily absorbed by a relatively thick insulating diaphragm which is hermetically sealed outside of the high pressure fluid by means of a thin metal diaphragm which is substantially coextensive with and in contact with the thick insulating diaphragm, and welded or otherwise bonded to the fitting which includes the high pressure chamber connected to the source of high pressure fluid.
However, at the ultra-high pressures handled by the present transducer, the compressive strength of the ceramic insulating diaphragm may be inadequate; therefore, the type of high-pressure transducer based on the principles disclosed in U.S. Pat. No. 4,617,607 may not be entirely suitable for ultra high pressures without significant improvement.
Accordingly, a principal object of the present invention is to provide an inexpensive ultra high pressure transducer.